Application of Amiet's theory for noise prediction of general airfoil profiles subjected to spanwise-varying inflow conditions

Abstract

In this paper, three different techniques are combined to provide a complete physics-based semi-anytical model for leading-edge noise prediction. The model is based on the classical theory of Amiet. Here, the two-dimensional turbulence spectrum is computed by a model based on the rapid distortion theory and the aeroacoustic transfer function is numerically evaluated by the boundary element method to account for the effects of the general airfoil profiles. The influence of spanwise inhomogeneities is also considered through the application of the inverse strip method. An assessment of each individual technique on the radiated noise is provided. This research shows that the turbulence distortion occurring at the leadingedge plays a significant role on the predicted noise levels. Compared with the von Karman model for isotropic turbulence, the rapid distortion theory predicts reduced noise levels at high-frequencies and increased levels at low-frequencies. This paper also shows that the spanwise-varying inflow, here represented by a linearly varying condition, contributes to raising the acoustic radiation when compared to the similar uniform inflow case. By considering modifications on the airfoil leading-edge radius and on the airfoil overall thickness, we show that the leading-edge bluntness plays a key role on reducing gust-airfoil interaction noise. This observation is more pronounced for microphones positioned downstream of the airfoil and for high frequencies.